A RAID controller is a hardware or software component that manages the Redundant Array of Independent Disks (RAID) configuration in a computer system. Its primary function is to combine multiple hard drives into a single unit, improving data redundancy and performance. By distributing data across several disks, RAID controllers help protect against data loss in case of a drive failure. There are different types of RAID levels, such as RAID 0, RAID 1, and RAID 5, each offering various balances of speed and data protection. RAID controllers can be found in servers, workstations, and high-performance computing systems, making them essential for data management in many environments.